Habib Mahmoud, managing editor for the state-linked Al-Sharq newspaper in Qatif, said the local Red Crescent authorities confirmed that 19 people had been killed and 28 wounded.

There was no immediate word from the Interior Ministry on casualties. The area is heavily populated by members of Saudi Arabia's Shiite minority.

The Interior Ministry initially reported that an explosion struck a mosque in the eastern province of Qatif after Friday prayers, without providing further details. It later confirmed that a suicide bomber who hid the explosives under his clothes was behind the attack.

It is the second deadly attack against Shiites in the kingdom in six months. In November, Islamic State was accused of being behind the shooting and killing of eight worshippers in the eastern village of al-Ahsa.

Interior Ministry spokesman Major General Mansour al-Turki said the latest attack struck the Imam Ali mosque in a village called al-Qudeeh.

A local activist, Naseema al-Sada, said the bomber targeted worshippers as they were commemorating the birth of Imam Hussain, a revered figure among Shiites. She said the local hospital called on residents to donate blood.

Lebanon's Al-Manar television channel, run by the Shiite Hezbollah group, carried blurry pictures of pools of blood inside what appeared to be the mosque where the attack took place. It also showed photos of at least three bodies stretched out on red carpets, covered with sheets. One person dressed in a white robe was being carried away on a stretcher.

Mr Mahmoud said the attacker stood with the worshippers during prayer and then detonated his suicide vest as worshippers were leaving the mosque.

Shiite residents in eastern Saudi Arabia have long complained of discrimination. They say that despite the region being home to most of the kingdom's oil reserves, their streets, buildings and infrastructure are in poor condition. They also say unemployment runs high among Shiite youth in the area.

In 2011, Shiites in the east inspired by the Arab Spring uprising in neighbouring Bahrain took to the streets to demand greater rights. Police arrested hundreds of people and a counter-terrorism court sentenced an outspoken cleric, Nimr al-Nimr, to death.

Qatif's residents say Saudi Arabia's air strikes against Shiite rebels in Yemen have inflamed sectarian tensions. Since the Saudi-led offensive began in late March, many leading Sunni clerics in the kingdom have used Friday sermons to denounce the Houthi rebels and their Iranian backers, but also to criticise their practices of praying at tombs and shrines.

After the bombing, a few hundred people marched in mourning through the village, Mr Mahmoud said.

Many conservative Sunni Muslims in Saudi Arabia, also known as Wahhabis, view the Shiite practice of praying at the tombs of religious figures as akin to polytheism.

The country's leading cleric, Grand Mufti Abdel-Aziz al-Sheikh, said the attack in Qatif aims at "driving wedge among the sons of the nation" and described it as "a crime, shame and great sin".

A group purporting to be a newly established Saudi affiliate of the Islamic State group said it was behind the attack.

In a statement distributed on IS-linked Twitter feeds, a group purporting to be the IS branch in Saudi Arabia issued the claim. It could not be independently confirmed if the new group has operational links to IS.

The group's statement carried a logo in Arabic referring to itself as the "Najd Province" - a reference to the historic region that is home to the capital Riyadh and the ruling Al Saud family, as well as the ultra-conservative Wahhabi branch of Islam.